It is well known in the art that complexes of nickel with phosphorous-containing ligands are useful as catalysts in hydrocyanation reactions. Such nickel complexes using monodentate phosphites are known to catalyze hydrocyanation of butadiene to produce a mixture of pentenenitriles. These catalysts are also useful in the subsequent hydrocyanation of pentenenitriles to produce adiponitrile, an important intermediate in the production of nylon. It is further known that bidentate phoshite and phosphinite ligands can be used to form nickel-based catalysts to perform such hydrocyanation reactions.
U.S. Pat. No. 3,773,809 describes a process for the recovery of Ni complexes of organic phosphites from a product fluid containing organic nitriles produced by hydrocyanating an ethylenically unsaturated organic mononitrile such as 3-pentenenitrile through extraction of the product fluid with a paraffin or cycloparaffin hydrocarbon solvent. It describes that the ratio of mononitrile to dinitrile must be 0.65 or less to obtain effective recovery, with efficiency improving as the ratio is reduced. Therefore, when hydrocyanation reaction conditions produces a mononitrile to dintrile ratio greater than 0.65, mononitrile must be removed from the product mixture before extraction is performed.
In contrast to the recovery of catalyst comprising monodentate phosphites and Ni, we have observed that Lewis acids utilized as promoters in the hydrocyanation reaction inhibit the effective recovery of diphosphite-nickel catalysts. It is therefore desirable to find conditions underwhich this inhibiting effect is reduced or eliminated.
There is a desire to provide better methods for recovering Ni diphosphite complexes in such a manner that minimal equipment and additional extraction solvent is required.
It is another object of this invention to be able to recover the complexes and operate the extraction in such a way that there is a broad composition range of the reactor product from which the catalyst is to be recovered. A further object of the invention is to delineate operating conditions whereby economical recovery of the catalyst is feasible.
Further objects, features, and advantages of the invention will become apparent from the detailed description that follows.